A wide variety of electrical components have become part of everyday life. In a typical day, a person may use an alarm clock, a computer, a television, and countless other electrically powered tools and appliances. The electric current used to operate each of these components produces both electric fields and magnetic fields, collectively referred to herein as electromagnetic (EM) fields.
As current passes through a conductor, the conductor acts like an antenna to transmit EM fields into the surrounding environment, much like a radio transmission antenna. Conversely, when a conductor is placed in an EM field, current is generated in the conductor, much like a radio reception antenna. So, the EM fields emitted by one electric component can induce electric current, or electromagnetic interference (EMI), in another electric component. Also, depending on the frequency of the emissions, EMI is sometimes also referred to as radio frequency interference (RFI). If the amplitude of the EMI is high enough, it may disrupt normal operations of circuitry. In order to ensure that electrical components can operate in close proximity to one another, various governing bodies, such as the Federal Communications Commission (FCC) in the United States, impose restrictions on EMI or RFI.
Printed circuit boards (PCBs), to which integrated circuits are coupled, can generate relatively large amplitude EMI. For instance, a power plane and a ground plane in a PCB act like antennas. For each clock cycle of an integrated circuit, numerous transistors may simultaneously draw current off the power plane or drive current onto the ground plane. These simultaneous current fluctuations from the power plane or onto the ground plane can cumulatively create large amplitude EMI emissions.
Noise on the power and ground planes also couples into the integrated circuits attached to the PCB. If this noise is too large, it may cause an error in the integrated circuit which will result in improper operation of an electronic device. These types of errors can be intermittent and, therefore, very difficult to determine their cause. These types of intermittent failures happen much more than users or even designers realize. Since they are very difficult to detect, it is better engineering design practice to minimize the power/ground plane noise that can cause them.
As transistor densities increase for integrated circuits, the EMI and noise restrictions become increasingly difficult to meet. Various cost-added techniques, such as noise filtering, can reduce or attenuate EMI and noise from PCBs. Large copper planes, however, and ground planes in particular, are very difficult to filter effectively, making power and ground planes large contributors to EMI and noise. Therefore, a need exists for reducing or attenuating EMI emissions and noise from power and ground planes. There is also a need to improve the performance of power and ground planes without significantly increasing the cost of printed circuit boards. These and related problems are addressed by the present invention.